Absorbent article with dual core

ABSTRACT

The absorbent article includes a topsheet having a body contacting surface, a backsheet joined to said topsheet, and an absorbent core disposed between the topsheet and the backsheet, wherein the absorbent core has a first absorbent core comprising a first area and a second area, wherein the first absorbent core and the second absorbent core are vertically arranged, wherein the second absorbent core at least partially covers the second area of the first absorbent core, and wherein the first absorbent core and the second absorbent core are different from each other at least in composition, density or absorption capacity thereof.

FIELD OF INVENTION

This application relates to absorbent articles, such as sanitarynapkins, for the absorption of menses, diapers, adult incontinenceproducts. More particularly, the present invention relates to absorbentarticles utilizing multiple absorbent cores which is cost effectivewithout compromising absorbency performance as well as comfort.

BACKGROUND OF THE INVENTION

Absorbent articles, such as sanitary napkins, diapers, adultincontinence products, and the like, are designed to be worn in closeproximity to the crotch of the wearer. Absorbent articles need toprovide for fluid acquisition and retention and need to be comfortableto wear, and usually comprise an absorbent structure having the capacityto acquire large amount of liquid under a short period of time.

Upon usage of such absorbent articles, it is desirable that they arethin and discreet to wear, and that they at the same time rapidly canacquire and store a large amount of liquid discharged during a shortperiod of time and then store this liquid in the article.

One method to improve absorbency is to increase the width or thicknessof the absorbent article. However, this approach may compromise withless comfortable pad for the consumer as the body is naturally narrow inthe front region and becomes broader towards the back while the pudendalregion is found in the front and most of the discharge exits the body inthe front region. This creates a tradeoff between comfort and increasedprotection.

Another approach to improve absorbency is to adopt multiple core layerswhere at least an additional absorbent core is placed on a bottomabsorbent core to cover at least a partial region of a surface of thebottom absorbent core which requires higher absorbent capacity thanother regions. This approach may not be cost effective by using extraabsorbent core material as the entire region having multiple core layersmay not require the increased absorbent capacity resulted from employingthe multiple core layers.

Accordingly, there is a continuing need for an absorbent article whichis cost effective while not sacrificing absorbency and comfort.

SUMMARY OF THE INVENTION

The present invention provides an absorbent article having alongitudinal centerline, a transverse centerline and a central pointwhere the longitudinal centerline and the transverse centerline cross,comprising a liquid permeable topsheet, a liquid impermeable backsheetjoined to the topsheet, an absorbent core disposed between the topsheetand the backsheet, wherein the absorbent core comprises a firstabsorbent core comprising a first area and a second area wherein thesecond area has a lower absorption capacity than the first area, and asecond absorbent core having a periphery, wherein the first absorbentcore and the second absorbent core are vertically arranged, wherein thesecond absorbent core at least partially covers the second area of thefirst absorbent core, wherein the first absorbent core and the secondabsorbent core are different at least in their composition, density,absorption capacity, opacity, color, flexibility, or resistance tocompression or bunching.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter of the present invention, itis believed that the invention can be more readily understood from thefollowing description taken in connection with the accompanyingdrawings, in which:

FIG. 1A is a plan view of an embodiment of an absorbent articleaccording to the present invention.

FIG. 1B is a cross section of an absorbent article as indicated bysection 1B-1B of FIG. 1A.

FIG. 1C is a cross section of an absorbent article as indicated bysection 1C-1C of FIG. 1A.

FIG. 2A is a plan view of an example of a first absorbent core of anabsorbent core of an absorbent article according to the presentinvention.

FIG. 2B is a plan view of another example of a first absorbent core ofan absorbent core of an absorbent article according to the presentinvention.

FIG. 3 is a plan view of an example of a second absorbent core of anabsorbent core of an absorbent article according to the presentinvention

FIG. 4A is a plan view of another embodiment of an absorbent articleaccording to the present invention.

FIG. 4B is a cross section of an absorbent article as indicated bysection 4B-4B of FIG. 4A when a second area of a first absorbent core isa void area.

FIG. 4C is a cross section of an absorbent article as indicated bysection 4C-4C of FIG. 4A when a second area of a first absorbent core isa void area.

FIG. 5A is a plan view of another embodiment of an absorbent articleaccording to the present invention.

FIG. 5B is a cross section of an absorbent article as indicated bysection 5B-5B of FIG. 5A when a second area of a first absorbent core isa void area.

FIG. 5C is a cross section of an absorbent article as indicated bysection 5C-5C of FIG. 5A.

FIG. 6A is a plan view of another embodiment of an absorbent articleaccording to the present invention.

FIG. 6B is a cross section of an absorbent article as indicated bysection 6B-6B of FIG. 6A when a second area of a first absorbent core isa void area.

FIG. 6C is a cross section of an absorbent article as indicated bysection 6C-6C of FIG. 6A.

FIG. 7A is a plan view of another embodiment of an absorbent articleaccording to the present invention.

FIG. 7B is a cross section of an absorbent article as indicated bysection 7B-7B of FIG. 7A.

FIG. 7C is a cross section of an absorbent article as indicated bysection 7C-7C of FIG. 7A.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term “absorbent articles” includes disposablearticles such as sanitary napkins, panty liners, diapers, adultincontinence articles, and the like.

As used herein, the term “absorbent core” refers to a component of anabsorbent article that is primarily responsible for the liquid handlingproperties of the article, including acquiring, distributing, andstoring body liquids. As such, the absorbent core typically does notinclude the topsheet or backsheet of the absorbent article.

As used herein, the term “asymmetric” means having no symmetry about atleast one axis.

As used herein, the terms “body liquid”, “body liquids”, “body fluids”,or “body exudates” include, but are not limited to menses, vaginaldischarges, blood, sweat, urine and combinations of these substances.

As used herein, the term “flexible” refers to materials which arecompliant and readily conform to the general shape and contours of thewearer's body under normal body-imposed forces.

As used herein, the term “foam” is synonymous with the term “cellularpolymer”, which includes materials having a significant void volume,typically greater than 75%. “Open-celled” foams further have areticulated internal structure disposed therein comprising relativelythin “strut” elements interconnected and forming cells or poresproviding for fluid communication throughout the structure.

As used herein, “hydrophilic” refers to a material or substance havingaffinity for water or aqueous fluids. In general, a hydrophilic surfacewill have a contact angle with water of less than 60°, or even less than30°.

As used herein, the term “inorganic” refers to a material which is notorganic in nature. As used herein, the term “organic” refers tocompounds of carbon.

As used herein the term “joined” refers to the condition where a firstmember is attached, or connected, to a second member either directly orindirectly. Where the first member is attached, or connected, to anintermediate member which in turn is attached, or connected, to thesecond member, the first member and second member are joined indirectly.

As used herein, the term “layer” refers to a three dimensional structurehaving two dimensions that are substantially greater than the thirddimension. The term layer is not limited to single layers or sheets ofmaterial. Thus a layer may comprise laminates or combinations of severalsheets or webs of the requisite type of materials. Accordingly, the term“layer” includes the terms “layers” and “layered.”

As used herein, the term “microfibers” refers to fibers having anaverage effective diameter of 0.1 micron to 6 microns and an aspectratio of at least 100. The aspect ratio of a microfiber is the contourlength of the fiber divided by the average effective diameter of thefiber. The contour length of a fiber is the length of the fiber in asubstantially straightened condition. Long microfibers can have aspectratios which exceed 1×10¹². The microfiber may be of any configuration,including but not limited to straight, curled, kinked, crimped, andcombinations thereof. The cross sectional area of the microfiberorthogonal to its contour length at any point may have any geometricshape, including but not limited to circular (round), square, flat,oval, star-shaped, irregular, and combinations thereof. For fibershaving a non-circular cross cross section, the effective diameter is thediameter of a circle having a cross sectional area equal to that of thefiber. Microfibers may comprise any material, including but not limitedto natural polymers, synthetic polymers, minerals, glass, ceramics,metals, vegetable matter, animal matter, carbon, and combinationsthereof. A sample of microfibers having an average effective diameterdiameter between 0.1 and 6 microns may contain individual fibers withdiameters greater than 6 microns and/or individual fibers with diametersless than 0.1 micron.

“Non-biopersistent” refers to microfibers comprising at least 18%alkaline and alkaline earth oxides and meets at least one of thecriteria for lack of biopersistence listed below. A non-biopersistentmaterial according to the present invention can also meet the criteriaof the German Dangerous Substances Ordinance (Gefahrstoffverordnung)Annex V, No. 7.1(1). A suitable method for selecting a fiber compositionto test for non-biopersistence of certain fibers according to the testmethod below is to use the method reported by Eastes, W., Potter, R. M.,and Hadley, J. G. (2000), “Estimation of Dissolution Rate from In-VivoStudies of Synthetic Vitreous Fibers,” ‘Inhalation Toxicology, 12(11),1037-1054. An online calculator implementing the method can be found athttp://fiberscience.owenscorning.com/kdisapp.html. This calculatorpredicts the rate of biodissolution as a function of the chemicalcomposition of the fiber. A non-biopersistent fiber meets at least oneof the following criteria: (1) a short-term biopersistence test byinhalation showing that the fibers longer than 20 um have a weightedhalf-life of less than 10 days (a suitable short-term biopersistencetest by inhalation is described in European Union protocol ECB/TM/26rev. 7), or (2) a short-term biopersistence test by intratrachealinstillation showing that the fibers longer than 20 um have a weightedhalf-life less than 40 days (a suitable short-term biopersistence testby intratracheal instillation is described in European Union protocolECB/TM/27 rev. 7), or (3) an appropriate intraperitoneal test showing noevidence of excess carcinogenicity (a suitable test for carcinogenicityof inorganic vitreous microfibers after intra peritoneal injection inrats is described in European Union protocol ECB/TM/18(97)), or (4) asuitable long-term inhalation test showing the absence of relevantpathogenicity or neoplastic changes (A suitable long-term inhalationtest is described in European Union protocol ECB/TM/17(97)). These testmethods are reported in European Commission Joint Research CentreInstitute for Health and Consumer Protection Unit: Toxicology andChemical Substances, European Chemicals Bureau (1999), “Methods for theDetermination of the Hazardous Properties for Human Health of Man MadeMineral Fibres (MMMF),” Report 18748, David M. Bernstein and Juan M.Riego Sintes Eds.

As used herein, the term “superabsorbent” refers to a material capableof absorbing at least ten times its dry weight of a 0.9% saline solutionat 25° C. Superabsorbent polymers, without being bound by theory, mayabsorb fluid via an osmotic mechanism to form a gel. Superabsorbents maybe particulates, fibers, foams, sheets, or other shapes.

As used herein, the term “symmetry” refers to an exact correspondence ofform and constituent configuration on opposite sides of a dividing lineor plane or about a center or an axis.

An absorbent article according to the present invention comprises aliquid permeable topsheet; a liquid impermeable backsheet joined to thetopsheet and an absorbent core disposed between the topsheet and thebacksheet. The absorbent core comprises a first absorbent core having aupper surface, a first area and a second area wherein the first area andthe second area are horizontally arranged and the second area has alower absorption capacity than the first area, and a second absorbentcore having a periphery. The first absorbent core and the secondabsorbent core are different from each other at least in one propertyselected from the group consisting of composition, density or absorptioncapacity, opacity, color, flexibility, or resistance to compression orbunching. In one embodiment, an absorbent article according to thepresent invention may be designed to have a predictable body fit whenworn and to have a second core with higher flexibility and/or reistneceto bunching than a first core which may reduce soailing and/or fluidleakage. Flexsibility can be provided by employing a different corematerial or forming holes or slits on a core. In another embodiment, anabsorbent article according to the present invention may be designed tohave better color/strain control in a second core. The first absorbentcore and the second absorbent core are vertically arranged, and thesecond absorbent core at least partially covers a upper surface of thesecond area of the first absorbent core. The second area can be a voidarea.

Referring to FIG. 1A, the absorbent article 10 has a longitudinal axis Land a transverse axis T that meet at a central point C. The absorbentarticle 10 has a front point F and a back point B. The transverse axis Tis located by taking the midpoint between the absorbent article frontpoint F and the back point B.

The absorbent article may also be provided with additional featurescommonly found in sanitary napkins, including “wings” or “flaps” 60 asis known in the art.

The absorbent article may also has a secondary topsheet, often calledacquisition and/or distribution layer, between the topsheet and theabsorbent core to promote fluid transport from the topsheet to theabsorbent core. The absorbent article may further comprise a lotioncomposition and/or various visual signals, indicia, or other markingsprovided for example onto at least one of either upper or lower side ofthe topsheet, the absorbent core, the backsheet and/or any optionallayer.

In one embodiment, referring to FIG. 1A, and FIGS. 1B and 1C, crosssection views of the absorbent article 10 shown in FIG. 1A by section1B-1B and section 1C-1C, respectively, the absorbent article 10 has atopsheet 20 having an upper surface 32 and lower surface 35 opposite theupper surface 32, a liquid impervious backsheet 30 joined to thetopsheet 20, and an absorbent core 40 disposed between the topsheet 20and the backsheet 30. The backsheet 30 has an upper surface 43 and alower surface 44 opposite the upper surface 43. The absorbent article 10has an adhesive 82 on the lower surface 44 of the backsheet 30. Theabsorbent core 40 has a first absorbent core 41 comprising a first area411 and a second area 421, and a second absorbent core 42. The secondabsorbent core 42 is disposed to at least partially overlap in itsperiphery 66 with the second area 421 in a transverse direction of thefirst absorbent core 41. The first absorbent core 41 contains an uppersurface 46, a lower surface 48 opposite the upper surface 46, a firstarea 411 and a second area 421. The second absorbent core 42 contains anupper surface 36 and a lower surface 38 opposite the upper surface 36.The upper surface 36 of the second absorbent core 42 may be in directcontact with the lower surface 35 of the topsheet 20. The lower surface38 of the second absorbent core 42 is in contact with the upper surface46 of the first absorbent core 41. The lower surface 48 of the firstabsorbent core 41 is in contact with the upper surface 44 of thebacksheet.

In another embodiment, referring to FIG. 4A, and FIG. 4B and FIG. 4Cwhich are cross section views of the absorbent article 10 shown in FIG.4A, a second absorbent core 42 is disposed to overlap in its entireperiphery 66 with a second area 421 of a first absorbent core 41. Thesecond area 421 of the first absorbent core 41 is a void area, and alower surface 48 of the first absorbent core 41 may be in directlycontact with a upper surface 43 of a backsheet 30.

In another embodiment, referring to FIG. 5A, and FIG. 5B and FIG. 5Cwhich are cross section views of the absorbent article 10 shown in FIG.5A, the second absorbent core 42 is disposed to completely cover anupper surface of the second area 421 of the first absorbent core 41, andpartially overlaps in its periphery 66 with the first area 411. In theembodiment, the second area 421 of the first absorbent core 41 is a voidarea surrounded with the first area 411 on at least one side in atransverse direction.

In another embodiment as a variation of the embodiment shown in FIGS.5A, 5B and 5C, the second area 421 of the first absorbent core 41comprises a conventional core material explained under ABSORBENT COREbelow.

In another embodiment, referring to FIG. 6A, and FIG. 6B and FIG. 6Cwhich are cross section views of the absorbent article 10 shown in FIG.6A, the first absorbent core 41 further comprises the third area 431 inaddition to the first area 411 and the second area 421. The three areasmay be arranged horizontally in a longitudinal direction where thesecond area 421 is sandwiched between two side areas of 411 and 431. Thefirst area 411 and the third area 431 may be identical, or may differfrom each other at least in its composition, density or absorptioncapacity.

In a similar way, when the first absorbent core 41 comprises three areasin a transverse direction where the second area 421 is sandwichedbetween two side areas, both sides outside of the second area 421 in atransverse direction can be first areas 411, or one side is a first area411 and the other side is a third area 431. The first area 411 and thethird area 431 may be identical areas, or may differ from each other atleast in composition, density or absorption capacity.

In another embodiment, referring to FIG. 7A, and FIG. 7B and FIG. 7Cwhich are cross section views of the absorbent article 10 shown in FIG.7A, the second absorbent core 42 is disposed to completely cover theentire upper surface of second area 421 of the first absorbent core 41,and overlaps in substantially the entire periphery 66 with the firstarea 411 of the first absorbent core 41. In the embodiment, the secondarea 421 of the first absorbent core 41 is a void area, and it issurrounded by the first area 411. In another embodiment as a variationof the embodiment shown in FIG. 7A, the second area 421 of the firstabsorbent core 41 comprises a conventional core material explained underABSORBENT CORE below.

Topsheet

A topsheet in the present invention can be any known or otherwiseeffective topsheet material, provided that the material has appropriateliquid permeability and smoothness to the skin. The topsheet can be apolymeric film, a nonwoven, a woven fabric, a paper web, a tissue paperweb, a cellulosic web or a knitted fabric, or a multilayer laminate ofany of the aforementioned.

Polymeric films suitable for the topsheet can comprise thermoplasticpolymers having characteristic rheological properties which depend ontheir composition and temperature. Polymeric films can include materialsnormally extruded or cast as films such as polyolefins, nylons,polyesters, and the like. Such films can comprise thermoplasticmaterials such as polyethylene, low density polyethylene, linear lowdensity polyethylene, polypropylenes and copolymers and blendscontaining substantial fractions of these materials. Such films can betreated with surface modifying agents to impart hydrophilic orhydrophobic properties, such as imparting a lotus effect. Polymericfilms can be textured or otherwise altered by forming marcro marcrofeature and/or micro features from a strictly flat, planarconfiguration. As used in the present specification, macro features areelements that are visible to the unaided eye of a person having 20/20vision from a distance of 30 cm in lighting at least equal to theillumination of a standard 100 watt incandescent white light bulb. Microfeatures are elements that are not visible to the unaided eye of aperson having 20/20 vision from a distance of 30 cm in lighting at leastequal to the illumination of a standard 100 watt incandescent whitelight bulb, wherein the illumination source is within 10 ft andvertically above the viewing surface.

Nonwovens suitable for the topsheet can comprise unbonded fibers,entangled fibers, tow fibers, or the like. Fibers can be extensibleand/or elastic, and may be pre-stretched for processing. Fibers of thenonwoven can be continuous, such as those produced by spunbondedmethods, or cut to length, such as those typically utilized in a cardedprocess. Fibers can be absorbent, and can include fibrous absorbentgelling materials. Fibers can be bicomponent, multiconstituent, shaped,crimped, or in any other formulation or configuration known in the artfor nonwoven webs and fibers.

Nonwovens suitable for the topsheet can be any known nonwovenscomprising polymer fibers having sufficient elongation properties toform macro features and/or micro features on the nonwoven.

In general, the polymeric fibers can be bondable, either by chemicalbond (e.g. by latex or adhesive bonding), pressure bonding, or thermalbonding. Nonwovens for the topsheet can comprise about 100% by weightthermoplastic fibers. Nonwovens for the topsheet can comprise as littleas about 10% by weight thermoplastic fibers.

A laminate suitable for the topsheet can comprise two or more nonwovenor a combination of polymer films, nonwoven, woven fabrics, paper webs,tissue webs, or knitted fabrics. Not to be limiting, a laminate topsheetcan comprise two layers of film, two layers of nonwoven, or a layer ofnonwoven with a film.

The topsheet of an absorbent article according to the present inventioncan have various optional characteristics, as is known in the art. Forexample, the topsheet can have channels embossed or other texturedsurfaces therein to direct fluid flow. The topsheet may also have macrofeatures and/or micro features such as apertures and tufts. Referring toFIG. 1A, apertures apertures 24 can serve the additional benefit ofcapturing fluid and fluid components that would otherwise tend to runoff of the absorbent article 10 and possibly soil the garments of thewearer. For example, if fluid were to run off toward the longitudinalend of the absorbent article 10, apertures 24 could intercept the fluidas it progressed, permitting a relatively unobstructed passage to anunderlying absorbent core 40. These apertures 24 may also serve asindicia regarding the placement of the absorbent article 10 regardingthe pudendal region and the undergarment.

Backsheet

A backsheet of an absorbent article according to the present inventioncan be any known or otherwise effective backsheet material, providedthat the backsheet prevents external leakage of exudates absorbed andcontained in the absorbent article. Flexible materials suitable for useas the backsheet include, but are not limited to, woven and nonwovenmaterials, laminated tissue, polymeric films such as thermoplastic filmsof polyethylene and/or polypropylene, composite materials such as afilm-coated nonwoven material, or combinations thereof.

Absorbent Core

An absorbent core in the absorbent article according to the presentinvention comprises a first absorbent core comprising a first area and asecond area wherein the second area has a lower absorption capacity thanthe first area, and a second absorbent core having a periphery. Thefirst absorbent core and the second absorbent core are verticallyarranged, and the second absorbent core at least partially covers thesecond area of the first absorbent core.

As explained in the section of First Absorbent Core below, a second areaof a first absorbent core may comprise a void area. A void area hereinmeans an area empty and with no component of an absorbent article.

When a second area is a void area and the second absorbent core isconfigured to be placed within the void area, the configuration of thefirst absorbent core and the second absorbent core is still consideredbeing vertically arranged.

Referring to FIG. 1A, the absorbent core 40 can have additional featuresin the first absorbent core 41, the second absorbent core 42, or boththe first and second absorbent cores. Additional features in theabsorbent core 40 may include slits, slots, apertures and lateralstiffeners.

The first absorbent core 41 and/or the second absorbent core 42 can havea plurality of laterally-oriented slots 72 having an average gap widthof at least 1 mm prior to use. Slots 72 are considered laterallyoriented if they have a major vector component at the longitudinalcenter line L that is perpendicular to the longitudinal center line.Slots 72 can be substantially parallel, generally linear slots that areeach parallel to center line L, and, therefore, have no vector componentin the longitudinal direction. However, slots 72 can have otherconfigurations, including generally curved orientations. The firstabsorbent core 41 and/or the second absorbent absorbent core 42 may alsohave any number of holes 70. Absorbent core 40 can have additionalmodifications and features to facilitate desired bending and folding.For example, absorbent core 40 can have additional slits, apertures,perforations, lines of weakness, lateral stiffeners, and the like. Inparticular, in one embodiment a line of weakness such as perforationsperforations or a score line along at least a portion of thelongitudinal center line L can aid in proper formation of a raised humpor protrusions intended to improve skin contact in that are of theabsorbent article.

First Absorbent Core

A first absorbent core comprises a first area and a second area having alower absorption capacity than the first area. Herein, “lower absorptioncapacity” includes zero absorption capacity like the case when thesecond area is a void area as explained below. The first absorbent coremay be in any geometric shape commonly known.

A first area and a second area of a first absorbent core arehorizontally arranged. The surface area of the first absorbent coreherein means the entire surface area of an upper surface of the firstarea and an upper surface of the second area.

The second area of the first absorbent core may comprise a void area.When the second area comprises a void area, an area empty with nocomponent of an absorbent article, the void area is considered to have avirtual upper surface and lower surface extended from a upper surfaceand a lower surface of the first area, respectively. When a second areais a void area, the void area has a central point C within the voidarea. The void area is at least partially surrounded by a non-void areasuch as a first area of the first absorbent core.

A first absorbent core may further comprise a third area which maydiffer from the first area at least in its composition, density orabsorption capacity. When the first absorbent core has a third area, thethird area may differ from the second absorbent core at least in itscomposition, density or absorption capacity.

FIG. 2A and FIG. 2B show exemplary embodiments of the first absorbentcore 41. Referring to FIG. 2A and FIG. 2B, the first absorbent core 41of an absorbent core 40 comprises a first area 411 and a second area421, and has a longitudinal axis L1 and a transverse axis T1 that meetat a central point C1. The transverse axis T1 is located by taking themidpoint between the front point F1 and the back point B1 outermostperiphery points of the first absorbent core 41. T1 may overlay T. L1may overlay L.

The first absorbent core 41 is approximately no greater than 25000 mm²,16000 mm² 9000 mm², 4000 mm², 1000 mm², or even less total surface areaon any one surface, such as, for example approximately 2500 mm².Alternatively, the first absorbent core covers no greater than 95%, 90%,85%, 80%, 75%, 70%, 65%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, 25%, 20%,15%, or 10% of the backsheet 30. First absorbent core 41 is divided byT1 into first absorbent core section one 56 and first absorbent coresection two 58. First absorbent core section one 56 and first absorbentcore section two 58 may be asymmetric or symmetric relative totransverse center line T1. First absorbent core section one 56 may beequal to, wider than or narrower than second absorbent core section two58.

The first absorbent core can be formed from any suitable materials.Examples of such materials include multiple plies of creped cellulosewadding, fluffed cellulose fibers, wood pulp fibers also known asairfelt, textile fibers, a blend of fibers, a mass or batt of fibers,airlaid webs of fibers, a web of polymeric fibers, and a blend ofpolymeric fibers.

The first absorbent core can be made by air-laying the mixture of fibersand thermoplastic material. In general, air-laying can be carried out bymetering an airflow containing the fibers and thermoplastic material, insubstantially dry condition, onto a typically horizontally moving wireforming screen. Suitable systems and apparatus for air-laying mixturesof fibers and thermoplastic material are disclosed in, for example, U.S.Pat. No. 4,157,724 (Persson), issued Jun. 12, 1979, and reissued Dec.25, 1984 as Re. 31,775; U.S. Pat. No. 4,278,113; U.S. Pat. No.4,264,289; U.S. Pat. No. 4,352,649; U.S. Pat. No. 4,353,687; U.S. Pat.No. 4,494,278; U.S. Pat. No. 4,627,806; U.S. Pat. No. 4,650,409; andU.S. Pat. No. 4,724,980.

The first absorbent core may be specially designed to worksynergistically with the higher absorption performing second absorbentcore while minimizing the spread of fluid away from the second absorbentcore and towards the perimeter of the product.

The first absorbent core may comprise airlaid material. A method ofproducing an absorbent core comprising airlaid material is disclosed,for example, in U.S. Pat. No. 8,470,219. For example, cellulose fibersare continuously deposited by a hammer mill by a first former onto aconveyor belt as loose fleece, so that a layer of tangled cellulosefibers is produced. A further preformed cellulose fiber layer may bedeposited by a second former as a layer, and a third layer may be placedon by a third former. The individual fiber layers may also comprisedifferent fibers and varying fiber densities. Moreover, it is possibleto add superabsorbent polymers to the fibers to increase the absorptioncapacity. The superabsorbent polymer may also be added to the fibershomogeneously prior to the sprinkling. These cellulose fiber layers arestill uncompressed uncompressed to a large extent. These are commercialproducts which have been used in the hygiene field for some time andwhich have already been described. Superabsorbent polymer may be addedin designated zones or lanes. For example, superabsorbent polymer can beadded in the first area 411 and the second area 421 of the firstabsorbent core in different concentrations, or can be added in the firstarea 411 only. Selective addition of superabsorbent polymer can beachieved by a number of ways known to the art, like having two separatesuperabsorbent polymer guns and/or nozzles in the same or differentsuperabsorbent polymer enclosures, or having one superabsorbent polymergun/nozzle and having baffles internal or external to direct thesuperabsorbent polymer stream into multiple distinct lanes/zones. Acompression of cellulose fiber layer(s) for example by embossment isfollowed. Cellulose fiber fiber layers or superabsorbent polymer can bedisposed in such a designated area on a belt that will be a first areaof a first absorbent area.

The first absorbent core may feature two distinct density zones. Thefirst density zone is a low density acquisition zone designed tominimize after use fluid appearance differences with the secondabsorbent core. Below this upper acquisition zone is a second densityzone for mainly fluid storage that comprises of a higher density thanthe lower density acquisition zone. The density of the second densityzone is preferably between 1.5 times and 3 times the density of thefirst density zone. Even more preferred is a second density zone that isbetween 2 times and 3 times the density of the first density zone.

In a non-limiting embodiment, the airlaid material may comprise at leastone BiCo fiber. The BiCo fiber may be a thickness of about 3 DTex to 5DTex, provided that the BiCo provides appropriate integrity and volumeto the airlaid core.

Together the use of two BiCo fibers provides wet integrity to theoverall airlaid core material while allowing the final acquisition zonedensity to be controlled.

To ensure fluid not retained by the second absorbent core absorbentmaterial is sufficiently contained within the first absorbent corematerial, the first absorbent core, at least in the first area, may havesuperabsorbent polymers. Contents of superabsorbent polymer in the firstarea and the second area of the first absorbent core can be determineddepending on product design, and may different in the first area and thesecond area. The first area may contain superabsorbent preferably atleast 5%. The second area may contain less than 5% superabsorbentmaterial by weight of the first absorbent core material, preferablysubstantially no superabsorbent.

In one embodiment, the first absorbent core may have substantially nosuperabsorbent polymer within 10 mm, preferably 5 mm, either outward orinward direction from the periphery of the second absorbent core.

Second Absorbent Core

Referring to FIG. 3, the second absorbent core 42 has a longitudinalaxis L2 and a transverse axis T2 that meet at a central point C2, and aperiphery 66. The transverse axis T2 is located by taking the midpointbetween the front point F2 and the back point B2 outermost peripherypoints of the second absorbent core 42. The transverse axis T2 may ormay not overlay T and/or T1. Similarly, the longitudinal axis L2 of thesecond absorbent core 42 may or may not overlay the longitudinal axis L1of the first absorbent core 42 and/or the absorbent article longitudinalaxis L.

The second absorbent core may cover no greater than 10%, 15%, 20%, 25%,30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 80%, 85%, 90%, or 95% of aupper surface of the first absorbent core. Alternatively, the secondabsorbent core may be covered by no greater than 95%, 90%, 85%, 80%,75%, 70%, 65%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, 25%, 20%, 15%, or 10%of a lower surface of the topsheet. The ratio of the second absorbentcore to a upper surface of the first absorbent core or to the lowersurface of the topsheet can vary depending on size and/or shape of thefirst and/or second absorbent core, product shape, product size, thepresence of wings, etc.

Second absorbent core 42 is divided by a transverse axis T2 into secondabsorbent core section one 52 and second absorbent core section two 54.First absorbent core section one 52 and first absorbent core section two54 may be asymmetric or symmetric relative to the transverse center lineT2. Second absorbent core section one 52 may be equal to, wider than ornarrower than second absorbent core section two 54.

The second absorbent core 42 can be either asymmetric or symmetricrelative to the transverse center line T2. T2 may also be located 10 cm,8 cm, 6 cm, 5 cm, 4 cm, 3 cm, 2 cm or 1 cm away from T or T1 along thelongitudinal center line L2 towards the front or back of the absorbentarticle.

The second absorbent core 42 may be made of any material provided thatit exhibits an absorption capacity higher than either the second area421 or the first area 411 of the first absorbent core 41.

In a non-limiting example, the second absorbent core 42 can include opencelled foam. One exemplary open-celled foam, High Internal PhaseEmulsion (HIPE) foam, is produced from the polymerization of themonomers including the continuous oil phase of a HIPE. HIPE foams mayhave one or more layers, and may be either homogeneous or heterogeneouspolymeric open-celled foams. Homogeneity and heterogeneity relate todistinct layers within the same HIPE foam, which are similar in the caseof homogeneous HIPE foams or which differ in the case of heterogeneousHIPE foams. A heterogeneous HIPE foam may contain at least two distinctlayers that differ with regard to their chemical composition, physicalproperties, or both; for example layers may differ with regard to one ormore of foam density, polymer composition, specific surface area, orpore size (also referred to as cell size). For example, for a HIPE foamif the difference relates to pore size, the average pore size in eachlayer may differ by at least 20%, by at least 35%, and by at least 50%.In another example, if the differences in the layers of a HIPE foamrelate to density, the densities of the layers may differ by at least20%, by at least 35%, and by at least 50%. For instance, if one layer ofa HIPE foam has a density of 0.020 g/cc, another layer may have adensity of at least 0.024 g/cc or less than 0.016 g/cc, in certainembodiments at least 0.027 g/cc or less than 0.013 g/cc, and in stillother embodiments at least 0.030 g/cc or less than 0.010 g/cc. If thedifferences between the layers are related to the chemical compositionof the HIPE or HIPE foam, the differences may reflect a relative amountdifference in at least one monomer component, for example by at least20%, in certain embodiments by at least 35%, and in still furtherembodiments by at least 50%. For instance, if one layer of a HIPE orHIPE foam is composed of 10% styrene in its formulation, another layerof the HIPE or HIPE foam should be composed of at least 12%, and incertain embodiments of at least 15% styrene.

The use of a foam second absorbent core 42 that is smaller in totalsurface of the absorbent core 40 provides a higher absorbency area onlywhere it is needed the most, rather than on the entire surface of theabsorbent core 40. This enables cost savings since foam which isrelatively expensive is only used where it makes the biggest absorbencyperformance impact. The use of a smaller second absorbent core 42 mayalso act as a signal for improved placement. The creation of a visiblesecond absorbent core 42 that is smaller in surface area than the firstabsorbent core 41 allows the consumer to use the second absorbent coreas a marker to determine proper placement. For instance, a user canplace the absorbent article in the undergarment such that the secondabsorbent core 42 lines up with the user's pudendal region.

A HIPE foam having separate layers formed from differing HIPEs, asexplained in more detail below, provides a HIPE foam with a range ofdesired performance characteristics. For example, a HIPE foam includinga first and second foam layer, wherein the first foam layer having arelatively larger pore or cell size than the second layer, when used inan absorbent article may more quickly absorb incoming fluids than thesecond layer. The second foam layer having relatively smaller poresizes, as compared to the first foam layer, which exert more capillarypressure and drain the acquired fluid from the first foam layer,restoring the first foam layer's ability to acquire more fluid. HIPEfoam pore sizes may range from 1 to 200 μm and in certain embodimentsmay be less than 100 μm. The desired thickness of a HIPE will depend onthe materials used to form the HIPE, the speed at which a HIPE isdeposited on a belt, and the intended use of the resulting HIPE foam.The HIPE foam for the present invention may have a thickness of 0.8 mmto 3.5 mm.

The HIPE foams for the present invention are relatively open-celled.This refers to the individual cells or pores of the HIPE foam being insubstantially unobstructed communication with adjoining cells. The cellsin such substantially open-celled HIPE foam structures haveintercellular openings or windows that are large enough to permit readyfluid transfer from one cell to another within the HIPE foam structure.For purpose of the present invention, a HIPE foam is considered“open-celled” if at least 80% of the cells in the HIPE foam that are atleast 1 μm in size are in fluid communication with at least oneadjoining cell.

In addition to being open-celled, in certain embodiments HIPE foams aresufficiently hydrophilic to permit the HIPE foam to absorb aqueousfluids, for example the internal surfaces of a HIPE foam may be renderedhydrophilic by residual hydrophilizing surfactants or salts left in theHIPE foam following polymerization, by selected post-polymerization HIPEfoam treatment procedures or combinations of both.

A HIPE foam can be flexible and exhibit an appropriate glass transitiontemperature (Tg). The Tg represents the midpoint of the transitionbetween the glassy and rubbery states of the polymer. In general, HIPEfoams that have a higher Tg than the temperature of use can be verystrong but will also be very rigid and potentially prone to fracture.

HIPE foams intended for applications requiring flexibility shouldcontain at least one continuous region having a Tg as low as possible,so long as the overall HIPE foam has acceptable strength at in-usetemperatures. In certain embodiments, the Tg of this region will be lessthan 30° C. for foams used at ambient temperature conditions, in certainother embodiments less than 20° C. For HIPE foams used in applicationswherein the use temperature is higher or lower than ambient, the Tg ofthe continuous region may be no more than 10° C. greater than the usetemperature, in certain embodiments the same as use temperature, and infurther embodiments 10° C. less than use temperature wherein flexibilityis desired. Accordingly, monomers are selected as much as possible thatprovide corresponding polymers having lower Tg's.

The mean cell diameters for open-celled foams can be between 10 and1,000 microns. The mean densities of open-celled foams can be between 40kg/m3 and 100 kg/m3. Mean cell diameters refer to the diameter of thepores in the foam visible by microscopy. The pores tend to to berelatively spherical in shape and the mean diameter can be measured byusing microscopic techniques. One suitable technique is to use ascanning electron micrograph and measure the apparent mean diameter ofat least 25 representative cells to determine the mean. The density offoams can be determined using uncompressed samples of said foams devoidof contaminants such as water, and measuring the volume and weight ofthe foam. A cubic sample having an edge length greater than or equal to2 cm is practical.

The ability of a structure to “pull” fluid against an opposing force,such as gravity or against affinity for fluid of another substrate withwhich the structure is in intimate capillary contact, can becharacterized by the capillary pressure. The capillary pressure can becharacterized as the hydrostatic head at which the vertically wickedfluid loading is 50% of the free absorbent capacity under equilibriumconditions at 31° C. The hydrostatic head is represented by a column offluid (e.g., synthetic menses). The second absorbent core 42 can have acapillary pressure of 2 cm to 15 cm.

The open-celled foam disclosed herein can be used in an initiallycompressed state that expands to full volume as a function of wear timeand/or fluid loading. The foam may collapse after an insult of fluid asthe first absorbent core pulls fluid away from the foam.

Test

Absorption Capacity Excise a specimen 2.54 cm×2.54 cm (1.0 in×1.0 in) orequivalent area from the longitudinal and lateral center of the core.Pour 90 mL of saline solution (0.9% NaCl in deionized water) into a 100mL disposable Petri dish. Measure the thickness of the specimen using adigital caliper, for example model # GS-503 available from Ono SokkiTechnology Inc. (USA), using a 2.54 cm diameter foot with an appliedpressure of 0.69 kPa (0.1 psi). Center the specimen under the foot andlower the foot onto the specimen at approximately 2 mm/sec. Take thereading after pressure has been applied for 5 sec and report to thenearest 0.01 mm. Measure the mass of the specimen on an analyticalbalance and record as “dry weight” to the nearest 0.001 g. Immerse thespecimen into the saline for 15.00 min±0.01 min. Using tweezers, grasp acorner of the specimen to remove it from the saline and suspendvertically to drain for 2.00 min±0.01 min. Measure the mass of the wetspecimen and record as the “wet weight” to the nearest 0.001 g.Calculate the capacity as follows:

Absorption Capacity(g/g)=[wet weight(g)−dry weight(g)]/dry weight(g)

Absorption Capacity(g/cc)=[(wet weight(g)−dry weight(g)]/[dry surfacearea(cm²)×dry thickness(cm)]

Repeat for a total of 3 specimens and report as the mean to the nearest0.01 g/g and 0.01 g/cc.

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm.”

Every document cited herein, including any cross referenced or relatedpatent or application, is hereby incorporated herein by reference in itsentirety unless expressly excluded or otherwise limited. The citation ofany document is not an admission that it is prior art with respect toany invention disclosed or claimed herein or that it alone, or in anycombination with any other reference or references, teaches, suggests ordiscloses any such invention. Further, to the extent that any meaning ordefinition of a term in this document conflicts with any meaning ordefinition of the same term in a document incorporated by reference, themeaning or definition assigned to that term in this document shallgovern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

What is claimed is:
 1. An absorbent article having a longitudinalcenterline, a transverse centerline and a central point where thelongitudinal centerline and the transverse centerline cross, comprising;a liquid permeable topsheet, a liquid impermeable backsheet joined tothe topsheet, an absorbent core having an area disposed between thetopsheet and the backsheet, wherein the absorbent core comprises a firstabsorbent core comprising upper surface, a first area and a second areawherein the first area and the second area are horizontally arranged andthe second area has a lower absorption capacity than the first area, anda second absorbent core having a periphery, wherein the first absorbentcore and the second absorbent core are vertically arranged, wherein thesecond absorbent core at least partially covers the second area of thefirst absorbent core, and wherein the first absorbent core and thesecond absorbent core are different from each other at least in oneproperty selected from the group consisting of their composition,density, absorption capacity, opacity, color, flexibility, or resistanceto compression or bunching.
 2. The absorbent article of claim 1, whereinthe first absorbent core comprises two density zones.
 3. The absorbentarticle of claim 1, wherein the first absorbent core comprisessuperabsorbent polymer.
 4. The absorbent article of claim 1, wherein thesecond area of the first absorbent core contains superabsorbent polymerin a lower percentage by weight than the first area of the firstabsorbent core.
 5. The absorbent article of claim 3 or 4, wherein thesecond area of the first absorbent core comprises substantially nosuperabsorbent polymer.
 6. The absorbent article of claim 4, wherein thesecond area of the first absorbent core comprises substantially nosuperabsorbent polymer.
 7. The absorbent article of claim 1, wherein thesecond area of the first absorbent core is a void area, wherein thesecond area has the central point within the second area.
 8. Theabsorbent article of claim 1, wherein the second absorbent corecomprises an open celled foam.
 9. The absorbent article of claim 8,wherein the open celled foam comprises polyurethane.
 10. The absorbentarticle of claim 1, wherein the second absorbent core covers more than20% of the upper surface of the first absorbent core.
 11. The absorbentarticle of claim 1, wherein the second absorbent core covers more than30% of the upper surface of the second area of the first absorbent core.12. The absorbent article of claim 1, wherein the central point islocated within the second absorbent core.
 13. The absorbent article ofclaim 1, wherein at least part of the first area of the first absorbentcore and at least part of the second absorbent core overlap.
 14. Theabsorbent article of claim 1, wherein the first area of the firstabsorbent core and the second absorbent core are configured to overlapin the substantially entire periphery of the second absorbent core. 15.The absorbent article of claim 1, wherein the first area of firstabsorbent core and the second absorbent core are configured not tooverlap with each other.
 16. The absorbent article of claim 1, whereinthe first absorbent core has substantially no superabsorbent polymerwithin 10 mm at least one of outward or inward direction from theperiphery of the second absorbent core.
 17. The absorbent article ofclaim 1, wherein the first absorbent core has a transverse axis and thesecond absorbent core has a transverse axis, and the transverse axis ofthe first absorbent core and the transverse axis of the second absorbentcore are not consistent each other.
 18. The absorbent article of claim1, wherein the first absorbent core further comprise a third area ahigher absorption capacity than the first area of the first absorbentcore.
 19. The absorbent article of claim 18, wherein the third area ofthe first absorbent core differ from the second absorbent core at leastin their composition, density or absorption capacity.